The long-term goal of this research is to gain an understanding of the cellular and molecular events that lead to neuronal damage and death in Alzheimer's disease (AD). This project tests the hypothesis that beta- amyloid destabilizes cellular calcium homeostasis and thereby renders neurons more vulnerable to environmental insults. A hippocampal cell culture system will be used to examine the cellular and molecular mechanisms whereby beta-amyloid destabilizes neuronal calcium homeostasis, and potentiates excitatory amino acid neurotoxicity. Immunolocalization studies of AD brains are designed to determine whether the neuropathology of AD is consistent with the calcium destabilization hypothesis of beta- amyloid neurotoxicity. The first aim will test the hypothesis that beta- amyloid affects specific cellular systems for calcium homeostasis (NMDA receptors, calcium channels, Na+/Ca2+ exchanger, calcium binding protein, and calcium ATPase). The second aim is to determine whether endogenous beta-amyloid contributes to selective neuronal vulnerability in cell culture. The third aim is to establish whether the cytoskeletal manifestations of neuronal degeneration induced by beta-amyloid resemble the neurofibrillary pathology of AD. The fourth aim is to determine the relationships of beat-amyloid, NMDA receptors, and calcium-regulating proteins in the histopathology of AD. These aims will be accomplished using the following technologies: immunocytochemistry to localize beta- amyloid and calcium-regulating proteins in cell cultures and in AD brains; light and confocal laser scanning microscopy in living neurons; electron microscopy; fluorescence ratio imaging of intracellular calcium levels. Each of these techniques will be applied to neurons at different stages in the progression of the neurodegenerative process. Taken together, these studies will: (1) Provide insight into the cellular and molecular mechanisms whereby beta-amyloid destabilizes neuronal calcium homeostasis. (2) Tell us whether the cellular pathology of AD is consistent, at the molecular level, with the calcium-destabilization hypothesis. (3) Generate information that can be used to develop new approaches to preventing and treating the neuronal damage that is responsible for the progression of AD.